Fun game! The different weapons are cool and I liked the some of the weird sound effects, I think they fit with the art style. Some of them sounded like they were clipping, not sure, maybe it was just happening on my browser.
Probably going offscreen should be disallowed (I once got lost and couldn't go back xD), and interestingly I think at least some of the enemy ships did not have collisions, but in general it was fun. Nice game!